DE 298 24 260 U1 and the corresponding EP 0 999 398 B1 describes such a plug-in connector of the generic type in which the plug-in part has, as latching means, two latching arms which are formed integrally in one piece. The latching arms extend on diametrically opposite sides of the plug-in part with their free radially elastically moveable ends, in each case approximately parallel to the plugging axis in the direction opposed to the plug-in direction, i.e. in the release direction. When plugging in occurs, the latching arms engage with radial latching shoulders in corresponding latching contours within the receiving opening of the connector counterpart, an end activation section projecting outward from the receiving opening in each case so that the latching arms can be moved radially inward manually in order to release the latched connection. In this context, there is a description of a protective cap which can be plugged over the plug-in region from the outside in order to provide a seal against dirt. In addition, the protective cap also prevents undesired release of the plug-in part because, before the release activation of the latching arms, the protective cap firstly has to be removed because otherwise the latching arms or their activation sections are not accessible. This known embodiment requires a relatively large amount of installation space, and the protective cap is, as a separate part, subject to a considerable risk of being lost.
U.S. Pat. No. 5,988,706 A describes a pipe which can be plugged with one end into a receiving part. In order to secure the pipe, it has an upset radial annular bead against which a securing element, seated on the pipe and composed of sheet metal, acts. This securing element is composed of an annular part which surrounds the pipe and two spring elastic latching arms which are located diametrically opposite one another and engage behind a step within the receiving part. In order to secure against release, a further hollow cylindrical ring is additionally arranged in a displaceable fashion on the pipe. This ring can be pushed axially into the region of the securing element.
A very similar design is described in U.S. Pat. No. 5,806,898 A, in which case a profiled ring body is provided for securing purposes.
DE 37 10 853 A1 describes a plug-in connection for a pipe. In this context, a receiving part has a cylindrical annular space into which the pipe and a securing sleeve which surrounds it and is made of plastic can be introduced.
Finally, US 2003/0132631 A1 describes a further pipe connection with a sleeve-shaped securing element and a cap-like securing element composed of an elastic material. This securing element is specifically embodied in such a way that it can be fitted onto an angular region of the pipe.